The objective of this research is to accomplish a genetic analysis of complex traits of mice analogous to human infirmities such as susceptibility to tumorigenesis, to allergies, and to infectious diseases. The approach involves the development and study of recombinant inbred strains of mice. This approach is unique in both its power of genetic analysis and its applicability to the multidisciplinary problems of health science. The application of this new concept promises to accelerate progress in many areas of mammalian genetics.